Certain 2-amino-4,5,6,7-tetrahydro-6-aminobenzothiazoles are known to have dopamine D-2 activity and are therefore potentially useful as pharmaceuticals for the treatment of psychiatric disorders such as schizophrenia and Alzheimer's disease. One such compound, the dihydrochloride salt of (S)-2-amino-4,5,6,7-tetrahydro-6-(propylamino)-benzothiazole I (pramipexole), is marketed as a pharmaceutical for the treatment of Parkinson's disease. The numbering of pramipexole I is indicated below.

Processes for the preparation of 2-amino-4,5,6,7-tetrahydro-6-aminobenzothiazoles are disclosed in U.S. Pat. No. 4,843,086, U.S. Pat. No. 4,886,812 and patent applications WO 02/22590 A1 and WO 02/22591 A1. A procedure to these types of compound is also disclosed by C. S. Schneider and J. Mierau in J. Med. Chem., 1987, vol. 30, pages 494-498.
However, known processes for the preparation of 2-amino-4,5,6,7-tetrahydro-6-aminobenzothiazoles are not satisfactory, particularly for industrial scale manufacture, as they have been found to be low yielding and involve the use of hazardous and difficult to handle reagents such as bromine, hydrazine and potassium chromate.